1. Field
This application relates to a heater control device and method for controlling turn-on of a heater, as well as an image forming apparatus.
2. Description of the Related Art
A halogen heater is used as a fixing heater used for an electro-photographic image forming apparatus. The halogen heater has a characteristic that inrush current easily occurs. Therefore, a voltage drop occurs at a commercial power supply in synchronization with a turn-on timing of the heater, which causes a lighting device such as a fluorescent light to flicker. There is known, therefore, a phase control technology for suppressing inrush current to the heater.
Further, there is known a turn-on/off pattern control technology for controlling a turn-on (energize) pattern of the heater. The human eye is most sensitive to light fluctuations in the frequency range near 10 Hz having and its center at 8.8 Hz. With recent image forming apparatuses, the heater-on/off pattern is set so as to avoid the frequency range where the human eye is sensitive to flicker or such that frequency band is shifted to reduce flicker to a minimum.
When the phase control technology and the turn-on/off pattern control are combined for controlling the heater, it should be considered that it cannot improve frequency characteristics effectively with certain duty cycle during transition period from the phase control to turn-on/off pattern control. Moreover, it should be considered that it cannot reduce flicker effectively.